The invention relates to a cathode ray tube comprising an in-line electron gun with means for generating electrons and a lens system including two facing lens electrodes having apertures for allowing passage of electrons.
Such cathode ray tubes are known and are employed, inter alia, for television receivers and computer monitors.
In such a cathode ray tube, three electron beams are generated in the in-line electron gun, which electron beams extend in one plane, the in-line plane. These electron beams are deflected across a display screen in two mutually perpendicular directions by means of a deflection means. A color selection electrode, for example a shadow mask, is situated between the electron gun and the display screen. The electron gun accommodates a lens system having two lens electrodes between which, in operation, an electron-optical lens is formed. Customarily, the electron gun comprises a main lens system by means of which the electron beams are focused on the display screen, and the electron gun further comprises a pre-focusing lens system which is situated between the main lens system and the means for generating electrons.
Of great importance for the quality of the picture display is the quality of the lens system or lens systems. Relatively small deviations in the electron-optical lenses formed in and by the lens systems may adversely affect the picture quality.